1. Field of The invention
This invention relates to a casing assembly for electronic equipment, which is used to accommodate instruments, and the like, of the rack mount type; and, more particularly, to a structural improvement of the casing assembly.
2. Description of the Prior Art
Electronic equipment includes, for example, control devices as mounted in machine tools, control panels, etc. Since the casing assembly for such control devices is generally mounted internally, it is desirable that the size thereof be small. One example of a casing assembly is disclosed in Japanese Laid-Open Patent 1-200,699.
To decrease the size of the casing assembly, the following factors must be considered.
(i) Mounting of DIN rail
A casing assembly for electronic equipment is generally attached to a DIN (Deutsche Industrie Norm) rail or a wall body. In this regard, the casing assembly must have a mechanism for attaching the assembly to the DIN rail. This attaching mechanism, however, increases the overall size of the casing assembly, or becomes unnecessary when the casing assembly is attached to a wall body.
(ii) Heat release
Since electronic equipment includes an exothermic element, such as a power source, it is necessary to suppress the internal temperature to below a given level by releasing the heat. To attain heat release, conventional electronic equipment utilizes radiation and convection, but, not conduction. In the case of radiation and convection associated with the surface of the casing assembly, the amount of heat to be released is determined by the temperature difference and the surface area of the casing assembly. On the other hand, in the case of convection associated with the heated air inside the casing assembly which is made up of free convection and forced convection, the amount of heat to be released is determined by the opening area of the casing assembly which is available for free convection or by the size and number of fans, and the like, used for forced convection.
If the electronic components are densely packed into a smaller sized casing assembly without improving the heat releasing mechanism, the internal temperature will rise, since the power of heat release will decrease with decrease in size, for the same heating value. Thus, the range of surrounding temperatures in which the casing assembly is serviceable is narrowed. On the other hand, if the size of the casing assembly is selected so that a given cooling power is obtained, this limits the size reduction of the casing assembly.
(iii) Supporting of terminal mount and printed board
Conventional printed circuit boards are large in size and poor in rigidity, and are supported at both edges by guide grooves of the casing assembly, and screwed at a central portion. Since the rigidity of the printed board increases relatively as the size decreases, it is desirable to eliminate reinforcing members to thereby decrease the number of such parts.
Where two printed circuit boards are stacked , one printed board is screwed usually to the other. In this case, since some electronic components cannot be positioned at such screwed portion, the packaging density decreases, and the assemblying or screwing then presents a problem.
(iv) Mounting of programmer
The control device used in conjunction with an input device is called a "programmer". Depending on the direction the control device is extended, such as lateral or longitudinal, the programmer is attached to the control device in the lateral or longitudinal direction. The display direction of a display section, which comprises an LCD, or the like, provided in the programmer coincides with the mounting direction of the programmer relative to the control device. Generally, it is desirable or convenient for the user, if the display section of the programmer is easy to observe irrespective of the direction of mounting of the control device.
(v) Cover and Connection
A connector is mounted on the control device and is used to connect the programmer. Since the programmer is not always connected, it is usually covered with a protective covering to guard the contact element when not in use. If the protective covering is detachable, it is liable to become lost. On the other hand, if the covering is slidable or pivotable, it needs a dead space in which to move. Thus, the packaging space inside the control device is decreased, and the surface of the casing assembly loses its smooth appearance.
When the programmer is mounted together with the control device, it is connected to a connector via a latch provided on the programmer. This latch serves as a guide and retainer in relation to the connector. However, if a force is applied to the programmer, it is applied through the latch to the connector. Thus, reliability of the connection to the connector is degraded.
(vi) Attachinq of an extended module
An extended module is connected to a casing where additional functions are desired, in addition to the standard functions of a basic module of the casing assembly. In that case, it is desirable that the casing be uniform and a joint cable be placed inside the casing so as to not be visible from the outside. Since the connection of the extended module is made to only one casing, it is better to simplify the connection mechanism, for connecting the extended module, of the casing assembly.